The disclosure of Japanese Patent Application Nos. 2000-197733 filed on Jun. 30, 2000, 2000-209464 filed on Jul. 11, 2000 and 2000-213264 filed on Jul. 13, 2000 including the specification, drawings and abstract are incorporated herein by reference in their entirety.
1. Field of Invention
The invention relates to a cooling structure of a cylinder block.
2. Description of Related Art
In an engine cylinder block, a water jacket is formed around a cylinder bore wall. Engine-cooling water is circulated in the water jacket to cool the cylinder bore wall heated from the combustion chambers.
In this construction, the temperature of the cylinder bore wall is unlikely to become uniform. The reason for the temperature non-uniformity is as follows. With respect to the circumferential directions relative to the cylinder bore wall, the temperature of portions in contact with two side portions of the cylinder bores in the direction of alignment of the cylinder bores where the flow speed is great is lower than the temperature of inter-cylinder bore portions where the flow stagnates. With respect to the up-down direction relative to the cylinder bore walls, the temperature of upper portions of the cylinder bore walls closer to the combustion chambers is higher than the temperature of lower portions thereof. Furthermore, with respect to the directions of alignment of the cylinder bores, the temperature becomes higher toward a downstream side.
The non-uniformity of cylinder bore wall temperature gives rise to various problems including degraded fuel economy, increased emissions of unburned hydrocarbons (HC), etc. For example, if the cylinder bore wall temperature varies in the circumferential direction, the shape of a cylinder bore wall deviates from a circular shape, thus resulting in degraded follow-up characteristics of the piston and oil rings with respect to the bore wall internal surface. If the ring tension is increased in order to prevent degradation of the follow-up characteristics, the friction in sliding movements increases, resulting in degraded fuel economy. Furthermore, if the cylinder bore wall temperature varies in the up-down direction, the evaporation and combustion of fuel deposited on an intermediate portion of each bore wall in the up-down direction deteriorates in the case of, for example, a direct fuel injection gasoline engine or the like, thus resulting in degraded fuel economy, reduced torque, and increased emission of unburned hydrocarbons (HC).
To curb these drawbacks, a uniform cylinder bore wall temperature is desired. Although there have been various proposals of improvements made regarding a water jacket of a cylinder block itself for the purpose of improving the wall temperature distribution or the like, most of them cannot be easily applied to mass production in view of productivity, mold service life, strength, etc. Some proposals have been made for improving the cylinder bore wall temperature distribution by disposing, in the water jacket of a cylinder block, a spacer (a means for uniforming the bore wall temperature by partially filling a space of the water jacket) formed separately from the cylinder block.
For example, Japanese Utility Model Application Laid-Open No. SHO 57-43338 discloses a cylinder block in which a water jacket is formed around a borehole, and a spacer whose shape is different from the shape of the water jacket in the direction of a borehole axis but is identical to the water jacket shape in the circumferential direction is disposed in the water jacket.
In this structure, a sufficient amount of cooling water is supplied around an upper portion of the borehole that is close to the combustion chamber and therefore is exposed to high temperature, and the spacer is disposed near a lower portion of the borehole that is remote from the combustion chamber and therefore is not exposed to high temperature so that supply of an unnecessary amount of cooling water is eliminated. Therefore, the structure advantageously improves the cooling water supplying efficiency.
However, the cylinder block cooling structure described in Japanese Utility Model Application Laid-Open No. SHO 57-43338 and the like has the following drawbacks.
(1) Although the bore wall near the cooling water inlet is cooled by low-temperature cooling water, the cooling water temperature increases during the passage through the surrounding of the high-temperature bore wall, so that the cooling of the bore wall becomes insufficient near the cooling water outlet. Due to the different bore wall cooling efficiencies in the bore wall circumferential direction, the borehole non-uniformly deforms. As a result, the bore wall follow-up characteristic of the piston and the like deteriorates, and the friction increases, and the fuel economy deteriorates.
(2) In a cylinder block having an open structure in which a water jacket is formed continuously around a plurality of bores, inter-bore portions receive heat transferred from the adjacent bores, but are not supplied with sufficient amounts of cooling water. Therefore, the inter-bore portions tend to have higher wall temperature than other portions. Due to the different bore wall cooling efficiencies of the inter-bore portions and the other portions, the boreholes non-uniformly deform.
It is an object of the invention to provide a cooling structure of a cylinder block capable of improving the cylinder block cooling efficiency and the cooling uniformity.
A cooling structure of a cylinder block in accordance with a first mode of the invention includes a water jacket continuously extending around a cylinder bore wall so as to convey a cooling medium, and a mechanism that sets a cooling characteristic of the water jacket based on at least one of a variation in a temperature of a cylinder bore wall in a direction perpendicular to an axis of boreholes and a variation in a temperature of the cooling medium in the direction perpendicular to the axis of boreholes, passing around the bore wall.
The setting of the cooling characteristic of the water jacket may be accomplished by disposing a spacer in the water jacket.
In the first mode, the cooling characteristic of the water jacket is set based on at least one of variation in the bore wall temperature in the direction perpendicular to an axis of the cylinder borehole and variation in the temperature of the cooling medium temperature in the direction perpendicular to an axis of the cylinder borehol passing around the bore wall. Therefore, the cylinder bore wall temperature can be uniformed by enhancing the cooling at a site of high cylinder bore wall temperature and weakening the cooling at a site of low cylinder bore wall temperature. Hence, non-uniform deformation of a borehole can be reduced.
In a cooling structure of a cylinder block in accordance with a second mode of the invention, the position of cooling around the cylinder bore is changed in accordance with the state of engine load.
According to the second mode, since the cooling position around the cylinder bore is changed in accordance with the state of engine load, it is possible to prevent a lower portion of a cylinder bore-surrounding portion from having high temperature during a high-load engine operation, by cooling the lower portion of the cylinder bore-surrounding portion during the high-load engine operation.
In a still another mode of the invention, a portion of the spacer disposed in a cooling water inlet portion or a cooling water outlet portion of the cylinder block may have a structure for reducing the flow resistance.
According to this mode, since the portion of the spacer disposed in the cooling water inlet portion or the cooling water outlet portion of the cylinder block has a structure for reducing the flow resistance, the flow resistance of inflow and outflow of the cooling water with respect to the water jacket in the cylinder block is reduced, so that the drive efficiency of a water pump will improve. Furthermore, the inflow and outflow of the cooling water with respect to the water jacket becomes smooth and stable, thus giving good effect on the cooling uniformity.